Switzerland's Novartis is letting Bayer and other rivals have a look into the books of its animal health business to whet prospective buyers' appetite for the unit, four people familiar with the matter told Reuters. The financial sources said the suitors were conducting a due diligence assessment of the Novartis business. Combining Bayer's roughly $1.7 billion in veterinary drugs sales with Novartis' $1.1 billion would lift the German company to the number three or four spot in the global animal health market, where Zoetis, a former Pfizer unit, is in pole position.